Process of and apparatus for the treatment of pulp



Jan. 12, 1932. H. w. FRENCH 1,840,774

PROCESS OF AND APPARATUS FOR THE TREATMENT OF PULP Filed Nov. 29, 1929 2 Sheets-Sheet l HOBERT W FRENCH F|G.2. W

Jan. 12, 1932. w, FRENCH 1,840,774

PROCESS OF AND APPARATUS FOR THE TREATMENT OF PULP Filed Nov. 29, 1929 2 Sheets-Sheet 2 o ooooooooo oooooooooooooooo oooooooooooooooo no ooooooooooooo oo ooeoooooooooo no oooooononoooo ooooooooooooo onoooooooonoo on ooooooooooooo no 0000 oooooooo on 0000 oooooooo oooo oooo ooo oo oooo oooooooo oooooooo oooooaoo ooo one

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oooooooo oooooooo I'HOBERT W FRENCH a Guam 226M Patented Jan. 12, 1932 UNITED STATES PATENT OFFICE ROBERT W. FRENCH, OF ERIE, PENNSYLVANIA, ASSIGNOR TO HAMMEBMILL PAPER COMPANY, OF ERIE, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA PROCESS OF AND APPARATUS FOR THE TBEATMIEN T 01' PULP Application filed November 29, 1929. Serial No. 410,401.

The invention relates to an improvement in that phase of the pulp making process which has to do with the draining ofl and washing out from a body of pulp the acids 5 and other substances embodied in the digestive liquors used in the conversion of wood or similar materials into such pulp.

In processes of this sort, as applied to the paper-making industry, it is the common practice to subject a mixture of wood chips,

or similar raw material, and a digestion solution of some suitable form, usually containing a certain quantity of acid, to a sufficient temperature, under a considerable pressure,

to cook the mixture and effect disintegration or digestion of the raw stock. After the digestion. of the stock has been completed. the contents of the vessel in which the cooking operation has been carried out are blown into a large vat, commonly known as a blow pit. The pressure in the blow pit is substantially atmospheric so that the material ejected from the digestion chamber under the high pressure maintained therein is thrown with considerable force into the blow pit. Here the digesting liquor is allowed to drain off through the pulp to the bottom of the vat and a washing medium, such as water, may be introduced to aid in the removal of any of the remaining traces of the digesting liquor. The present invention has to do primarily with this phase of the process and apparatus employed in the manufacture of pulp.

()ne of the principal objects of the invention has been to improve the efliciency of operation of a blow pit connected with a pulp digester by speeding up the draining and washing actions carried out in the blow pit and by reducing the time required for removing the pulp from the pit after a blowing and washing operation has been completed.

Another important object of the invention has been to simplify the construction of blow pits and to reduce the cost of construction of equipment of this character having a given capacity. An incidental object has been to render the blow pits more readily accessible for purposes of inspection and repair.

@U Due to a lack of available space at points where installations of this sort are usually made, it has been the common practice heretofore to employ blow pits of rectangular form. This has enabled the installation of a series of digesters and its in a row in such a way as to take full a vantage of the space allotted to this part of the equipment. However, the use of pits of rectangular form has brought about certain complications in construction which have made them quite expensive. On account of the nature of the digesting liquor which, as has been mentioned, usuall contains a quantity of acid, it has been ound either necessary or desirable to construct the pits of wood. Now, in order to provide a liquid-tight joint at the corners of a rectangular form of pit, and to provide sufiicient strength at the corners to withstand the pressure of the contents of the pit, it has been necessary to resort to rather complex and expensive constructions at these points. Some attempts have been made to overcome this difliculty in a measure by providing a pit having an encasing wall of concrete which is merely lined with wood. This type of construction, however, is not only expensive but it has also presented difficulties in the wa of maintaining a liquid-tight lining. ere leaks have developed in the lining, the digesting liquor has found its way to the concrete structure and has caused considerable damage. Incidentally, it is very diflicult to detect leaks in a pit formed primarily of concrete and merely lined with wood since these leaks cannot be detected from the outside until considerable damage has been done and they are not, always apparent from the inside. I

I have overcome the difficulties inherent in the blow pit constructions previously employed by forming the pit in the shape of an oval or ellipse which Wlll fit within the space previously provided for a rectangular pit. This oval form of pit is not only simple and inexpensive to construct, but it is capable of withstanding the internal pressures more readily and where a series of such pits are placed in a row, they may each be readily inspected from theoutside so that leaks may be instantly detected. At the same time I have found that this form of pit possesses a number of advantages from an operating standpoint, including the more efiicient conduct of the draining, washing and cleaning out functions.

Other objects and advantages of the invention will appear from the detailed description which will now be given in conjunction with the accompanying drawings, in which:

Figure 1 is a plan View of the blow pit with thetopand some of the interior construction artly cut away and disclosing certain parts in section.

Figure 2 is a sectional elevation of the pit taken along the line 2-2 of Figure 1.

Figure 3 is an enlarged sectional elevation taken along the line 33 of Figure 1.

Figure 4 is an enlarged plan view of one of the draining tiles employed, and

Figure 5 is a section through the tile along the line 5-5 of Figure 4.

Referring now to the drawings, the blow pit is preferably provided with a reinforced concrete foundation desi nated 10, which may be either elliptical in orm or, for ease of construction, may present an octagonal or other polygonal surface, as indicated in F igure 1. On the surface of theconcrete foundation a series of timbers 11 are placed at suitable spaced intervals, running preferably parallel to the longer axis of the elliptical form of the pit. On these supporting timbers the floor boards 12 of the pit may be laid in such a way as to provide a liquid-tight surface of the desired elliptical form. Thesides of the pit-are formed of vertically disposed pieces of lumber 13 of suitable dimension for the desired strength and durability. Preferably, these side boards are provided with horizontal grooves 131 near the bottom to receive the edges of the floor boards 12 and thus provide a leak-proof joint. A plurality of hoops 132 formed of steel or other suitable material may encircle the entire side wall of the pit and retain the latter in place against the outward pressure of the contents of the pit. This construction does away with the necessity of providin vertical posts or supporting timbers whic are required in other forms of construction to assist in retaining the sides in place. The cover of the pit may be formed of suitable boards 14, similar to the floor boards, and having their ends adapted to fit into grooves 133 formed in the side members near their upper ends. A number aof cross beams 15 may be provided to strengthen the onstruction at top and these beams v ierably have g.ooves 151 into them ar their ends to recei 2 the upper ends of the side boards 13 to assist in retaining the latter in position.

At one end of the pit there is provided an opening through which a pipe or other transmission means 1:: from the digestion chamber of a pulp-making apparatus may be introduced. This opening is preferably above the maximum liquid level to be attained in the pit, as indicated by the line 17 in Figure 2, and should be to oneside of the major axis of the ellipse so as to permit the tangential introduction of the pulp. This will produce a whirling movement of the body of pulp, which tends to distribute it evenly over the entire surface of the pit.

Another effective method which may be employed to secure even distribution of the pulp may involve the use of a distributing plate against which the pulp is first thrown.

f this method is adopted the pipe 16 will preferably enter the pit at one end of the mainaxis and at the opposite end of the pit there will be mounted a deflector 18 which may be of any suitable form adapted to distribute over a large area the stream of pulp in solution which is blown directly against it from the pipe 16. The deflector may advantageously assume the form indicated in Figures 1 and 2 of the drawings, which consists of a double concave surface. However, this double concave form is not essential as very satisfactory results may be obtained through the use of a single concave element formed as a portion of a cylinder of proper diameter and situated directly opposite the opening 16 or at a slightly lower level in the pit. Along one of the sides of the elliptical it, near one end, there is provided an opening 19 preferably above the maximum liquid level within the pit and provided with a suitable door or closure. This opening is for the introduction of water, or any other suitable washing medium, which ma be employed to assist in washin out the acid and other constituents of the digesting liquor from the pulp undergoing treatment and to aid in the re moval of the pulp after the washing operation is completed. The water or other washing medium is preferably introduced through the opening 19 by means of a hose which is directed at a tangent to the wall of the pit so as to set up a whirling movement of the liquid and pulp at the surface. This aids both in the washing of the undesirable constituents from the pulp and in the removal of the pulp at the end of the operation.

In the top or cover for the pit a large opening 20 is provided to permit inspection of the interior of the pit and also to permit rapid introduction of largc volumes of water at the beginning of a blowing operation and for cleaning of the pit after the removal of the pulp following a blowing operation. If desired, this opening may be eliminated and all water for the purposes mentioned may be introduced through the opening 19. A suitable closure or cover should be provided for the opening 20 to prevent the escape of fumes and the like during use of the pit.

Another opening 21 is provided in the blow-pit to permit the introduction of a shower of water during the blowing period. For this purpose a suitable spray device may be inserted into the opening 21 or permanently mounted in the pit and connected to a source of \vatcr through the opening 21. The primary function of the water so introduced is to cool the incoming material and condense a portion of the steam contained in this ma terial. Steam which is not condensed and some which is formed on contact of the water with the hot material, together with fumes developed in the course of digestion of the pulp, may be carried away through an opening 22 in the roof of the pit and led through suitable ducts to a condensing and recovery system. The steam which is condensed in this way may be discarded, while the sulfur and other constituents of the fumes may be recovered. In lieu of providing the condensing and recovery equipment, the fumes and steam escaping through the opening 22 may, if desired, be permitted to pass to a stack and then into the atmosphere.

On the bottom of the pit there is provided a surface formed of drainage tiles 23 adapted to permit the removal of the water and other liquid which filters through the pulp to the bottom. The form of these tiles is best shown in Figures 4 and 5. A large number of perforations 24 is provided in each section of the tile to permit the passage of the water and other liquid but not the pulp. The upper tile surface is preferably elevated slightly above the wooden floor of the pit so as to form a pocket or space below it for the accumulation of the liquid as it filters through the pulp. For this purpose a series of spaced cross timbers 25 may first be laid flat on the floor of the pit. On these there may be a second series of timbers 26 placed on edge and spaced at suitable intervals along the base. These in turn may support a series of timbers 27 suitably spaced and extending longitudinally of the pit. The spacing of these last mentioned timbers is determined by the width of the tile members. A single tile member should extend from substantially the center of one of the timbers 27 to substantially the center of the next. The sides of the tile elements are preferably inclined slightly to the vertical, as shown, and a slight space is left between adjacent tile members for the insertion of slender. wooden wedge meinoers 28. These are preferably driven down between the adjacent tiles and are secured to the timbers 27 by any suitable means, as by brass screws or brads 29.

In this way substantially all of the surface of the bottom of the pit is provided with a smooth covering of tile, which is elevated about a foot from the normal floor of the pit. However, a small section 30 (Figures 1 and 3) is left without any tile covering so as to constitute a sump or well through which the pulp may subsequently be withdrawn. Suitable timbers 31 are provided to form the side walls of the sump in conjunction with a portion of the side wall of the pit. During a blowing and washing operation the water and other liquids, which are drained through the tiles 23 into the checker-work below, may be withdrawn from the pit through an opening 32 and passed to any suitable storage or recovery system or disposed of in any other way. An outlet 33 is provided from the sump 30 so that after a blowing and washing 0 ration has been completed, the pulp may e withdrawn from the pit. This outlet and the opening 32 are provided with valves or closures to prevent the passage of the pulp and liquids at undesired times during the blowing and washing operations.

A typical operation of the briefly explained as follows:

First let it be assumed that the pit is of substantial size commensurate with the usual rectangular pits, say, for example, having its longer axis 38 feet long, its shorter axis about 22 feet and its depth about 16 feet. Water is first introduced into the pit through the opening 20 until it reaches a depth of, say, 4 feet in the bottom of the pit. The opening 20 is then covered and the pulp which has been cooked to the proper degree in the digestion chamber is then blown through the pipe 16 under the pressure in the chamber and is blown with considerable force either tangentially to and along the wall of the pit. to create a whirl which distributes it evenly, or against the deflector 18. It will be understood that the pressure within the pit is substantially atmospheric and that the relatively large pressure drop brings about a high velocity in the stream of pulp entering the pit. The deflector will preferably be situated at a point slightly below the plane of the opening 16 and will preferably be vertically disposed. However, in lieu of this arrangement the deflector may be located at substantially the same level as the opening 16 and may be inclined slightly to the vertical so as to accomplish the same result in the way of distributing the pulp over the bottom of the pit. It will be found that due to the high velocity of the incoming stream of pulp it will be distributed quite evenly over the entire floor area. either as a result of its tangential introduction or on account of the action of the deflector, so that the draining action will be carried out at all points over the surface at a siibstantially even rate. This has not been possible where rectangular pits have been used since it is impossible in these older constructions to secure even distribution of the pulp in the corners. The corners, therefore, become practically a dead space which contributes little, if any, to the drainage function of the pit. During the blowing operation additional water is sprayed into the blow pit may be pit through the opening 21 to aid in cooling the mixture and further cleansing it. Steam generated in this way and the fumes developed in the process are carried awa through the opening 22, at the top, into the ucts leading to the condensers and recovery apparatus. After a desired quantity of the pulp has been blown into the pit, as when a digestion chamber has been emptied, an extra quantity of water or other washing medium is in-' troduced either through the opening 20-or by means of a hose through the opening 19. The introduction of this medium at a tangent to the Wall of the pit through the opening 19 in the manner explained serves to set up a whirling action in the body of pulp, digesting liquor, and washing water which aids materially in the washing action. All of the constituents are brought into much more intimate contact in this way and in consequence the washing action or removal of the acids and other portions of the digesting liquor is performed more efliciently. As the liquor and water filter through the pulp and then through the tiles 23, they will pass to the drain outlet 32 and may be disposed of in any suitable way. This outlet, however, will preferably be kept closed until the contents of the digestion chamber has been completely blown into the pit.

After the contents of a digester has been blown, drained and washed in the manner indicated over a sufficient period of time to effect adequate cleaning, the pulp may be removed from the pit and subjected to further steps in the process of paper manufacture. At this time the discharge outlet 33 leading from the sump is opened and the stream of water introduced through the opening 19 is permitted to flush the pulp out of the pit into the transfer line leading to the next step of the process. The oval form of the pit aids materially in the rapid removal of the pulp. There are no corners in which the pulp may become settled and from which it would be a difficult matter to dislodge it. When the pulp has been completely removed, the flushing or cleaning out of the interior of the pit is also rendered quite simple. The difiiculties heretofore encountered in the way of accumulations of dirt and other matter in the corners of a rectangular pit are completely obviated. Water may very readily be introduced through either A or both of the openings 19 and 20 for this cleansing operation.

During the course of an operation of the pit the exterior surfaces which are quite accessible may be observed from time to time so that any leaks which may develop may be detected and remedied during the next cleaning period. This inspection is greatly facilitated by the oval form of the pit and, as pointed out, the provision of some space between the pits of a series has done away merely with the inefiicient corners of the old rectangular form of pit and has not in any Way reduced the capacity of a unit confined to a givenspaee but has rather increased it.

While one admirable form of the invention has been set out in considerable detail, it is to be understood that man modifications in the construction may be ef ected without departing from the spirit and scope of the invention. For example, it has been stated as preferable to employ wood as the material of construction for the pit. While this is regarded as desirable, other materials may be employed to advantage so long as they are formed of, or coated with, substances which are not severely acted upon by the acids and other constituents of the digesting liquor. Many other possible changes falling within the scope of the invention will suggest themselves to one skilled in the art.

The invention has been disclosed in its illustrative form as being particularly applicable to the draining and cleaning of pulp produced in a paper-making process but it will be understood that it is of broader application. For example it may be employed in a similar way in the handlin of other forms of pulp, such as employe in the manufacture of artificial silk or other products of a cellulose base, or the like.

What I claim is:

1. A blow pit for use in the treatment of pulp comprising an enclosing wall of elliptical formation, an opening at one end of said wall through which a stream of pulp may be introduced, a distributing plate at the opposite end of said wall in the path of the stream of pulp, and an opening in said wall adapted to permit tangential introduction of a washing medium.

2. In apparatus for the treatment of pulp a blow pit of elliptical formation and means for distributing pul over the bottom thereof.

3. In apparatus or the treatment of pulp a blow pit of greater length than width having a side wall of a smooth continuously curving contour, an opening in said wall for the introduction of a stream of pulp, and means within'said pit for distributing the pulp evenly over the bottom thereof.

4. A blow pit for use in the treatment of pulp comprising an enclosing wall of ellip tical formation, a drainage surface provided at the bottom of said pit, means for evenly distributing paper pulp over said drainage surface, and an opening adapted to permit tangential introduction of a washing medium.

5. A blow pit for use in the treatment of pulp comprising an enclosing wall of elliptical formation, a drainage surface provided at the bottom of said pit, an opening in said wall above the normal maximum liquid level within said pit for the introduction of a stream of pulp thereto, a distributor plate in the path of said stream of pulp for spreading the latter over the bottom of the pit, and an opening in the enclosing wall above the normal maximum liquid level for the introduction of a washing medium at a tangent to said wall.

6. In a pulp treating process the steps comprising spreading digested pulp evenly over an enclosed drainage surface having curved retaining walls and introducing a washing medium at a tangent to the enclosing wall around said surface to set up a whirling action in the pulp.

7 A blow pit for use in the treatment of ulp which comprises a bottom of elliptical urination, vertical side walls conforming to the contour of the bottom, a top closure fitted within and supported by said side walls, and openings in said side walls for the introduction of pulp and a washing medium.

8. A blow pit for use in draining and washing pulp comprisin a concrete foundation, a substantially elliptical surface on said foundation formed of material resistant to the action of the pulp digesting liquor, side walls of similar material surrounding said surface, drainage tiles covering said surface, a cover for the pit fitted within and supported by said side Walls, retaining means surrounding said walls, and openings in said walls for the introduction of pulp and a Washing medium.

9. A blow pit for use in the treatment of pulp which comprises a side wall of substantially elliptical formation and means for introducing pulp into said pit at a tangent to the curvature of the wall.

10. A blow pit for use in the treatment of pul which comprises a side wall of substantial y elliptical formation, a tile drainage surface at the bottom of said pit and substantially covering the same, an untiled sump formed near a portion of the wall ofthe pit, means for introducing pulp and a washing medium tangentially into said pit, means for removing the liquid draining through said tiled surface, and means for withdrawing the pulp from the pit through said sump.

In testimony whereof, I have signed my name to this specification this 26th day of November, 1929.

HOBART W. FRENCH. 

